(1) Field of the Invention
This invention concerns a process and the equipment for the opening of folded proof sheets so as to enable their positioning on the conveyor plate of a thread stitching machine. A "signature" or stack of the proof sheets is moved along devices which serially separate portions of the individual sheets from the stack and the individual sheets are subsequently opened.
(2) Description of the Prior Art
The equipment presently known for the opening of folded layers of proof sheets, as exemplified by the disclosure of German Patent Publication No. 1,099,988, is a device with a conveyor belt beneath it on which a proof sheet is transported in its closed state. On either side of the conveyor belt is a pair of cylindrical suction rolls and beyond these suction rolls, in the direction of transport, is another pair of cylindrical suction rolls. Between the pairs of suction rolls are proof sheet diverters which form the transition from the vertical transport area of the first pair of suction rolls to the slanted mantle area of the second pair of suction rolls which guide the outer edges of the sheets, which were gripped by the first pair of suction rolls, to the area behind the proof sheet diverters. During further transport, the sheets are moved away from the effect of the second pair of suction rolls through the use of the proof sheet diverter and subsequent sheets are gripped and guided over further proof sheet diverters until the proof sheets thus opened are fed to the collating plate of another machine.
In order to open three or more single sheets which have been folded and inserted into one another, the required number of pairs of suction rolls can be arranged and connected with each other by proof sheet diverters.
Automatic programming permits starting and stopping the individual suction rolls in a predetermined sequence.
The device described and illustrated in aforementioned German Patent Publication No. 1,099,988 for the opening of folded layers of sheets is unsatisfactory in that it does not permit the opening of all kinds of layers. For instance, if the stack consists of sheets with square folding, e.g., if the layers are partially closed at the top or bottom, the suction rolls and proof sheet diverters cannot be guided through them. While it is in some cases possible to open squarely folded stacks on one side by guiding such stacks over suction rolls and proof sheet dividers of the type disclosed in German Patent Publication No. 1,099,988, the full opening of such a stack is possible only if the machine to which the sheets are fed has a cooperating feeding edge. This machine could, for instance, be a thread stitching machine and the feeding edge could either be located at its front or its back, depending upon the model.
However, practical experience has shown that one cannot open a great number of square folded layers with the device described in German Patent Publication No. 1,099,988.
Furthermore, the suction rolls used in the device of German Patent Publication No. 1,099,988 are not capable of processing every kind of paper. Due to the strong suction effect, several sheets tend to be sucked up at one time when porous paper is used, thus leading to significant problems in the production process.
German Pat. No. 1,945,501 discloses a device for the central opening of proof sheets which are folded at right angles wherein a sheet mover is fashioned as a conveyor belt which is positioned along a number of rotating suction devices, all the way to the opening area, for the lifting and turning of the free portions of the sheets not held by the conveyor belt. The apparatus of this patent also employs grippers which grip also the main fold of the free edge of the lower half of the opened proof sheet. The controlling of the suction effect can be done either by a photoelectric light barrier or by automatic programming. At the end of the conveyor belt, the proof sheets are put onto a collating plate such as that of the thread stitching machine whereby the free sections of the sheets, which are not being held by the conveyor belt, are held up by a guide plate.
The apparatus of German Pat. No. 1,945,501 can be used to open any conceivable layer of paper at the point desired, but it is not able to handle porous paper, at least not without problems.
Another shortcoming of the device of German Pat. No. 1,945,501 is the fact that due to the inherent stiffness of paper it does not permit the continuous turning of sheets which are of a small format and are closed either at the top or the bottom.
Furthermore, the opening devices according to German Patent Publication No. 1,099,988, as well as those described in German Pat. No. 1,945,501, are limited as to the amount by which the sequencing speed can be increased since the opening process of one opening station has to be completed before the next proof sheet can be taken.